Thirty years ago, half the developing world lived in extreme poverty today, a quarter. Now, a much smaller share of children are malnourished and at risk of early death. And access to modern infrastructure is much more widespread. Critical to the progress: rapid economic growth driven by technological innovation and institutional reform, particularly in today's middle- income countries, where per capita incomes have doubled. Yet the needs remain enormous, with the number of hungry people having passed the billion marks this year for the first time in history. With so many still in poverty and hunger, growth and poverty alleviation remain the overarching priority for developing countries. Climate change only makes the challenge more complicated. First, the impacts of a changing climate are already being felt, with more droughts, more floods, more strong storms, and more heat waves-taxing individuals, firms, and governments, drawing resources away from development. Second, continuing climate change, at current rates, will pose increasingly severe challenges to development. By century's end, it could lead to warming of 5°C or more compared with preindustrial times and to a vastly different world from today, with more extreme weather events, most ecosystems stressed and changing, many species doomed to extinction, and whole island nations threatened by inundation. Even our best efforts are unlikely to stabilize temperatures at anything less than 2°C above preindustrial temperatures, warming that will require substantial adaptation. High income countries can and must reduce their carbon footprints. They cannot continue to fill up an unfair and unsustainable share of the atmospheric commons. But developing countries whose average per capita emissions are a third those of high income countries need massive expansions in energy, transport, urban systems, and agricultural production. If pursued using traditional technologies and carbon intensities, these much-needed expansions will produce more greenhouse gases and, hence, more climate change. The question, then, is not just how to make development more resilient to climate change. It is how to pursue growth and prosperity without causing "dangerous" climate change.